London: People who have lower core body temperatures have a reason to rejoice as they are destined to live a long life. According to a study, slowing metabolism extends lifespan.

Researchers at the Washington University School of Medicine in St. Louis found a link between lower core body temperature and a longer lifespan.

It was discovered that people who eat less have lower core body temperatures compared to those who eat more.

They suspect that the hormonal changes that conserve energy and heat - by slowing down metabolism -- also extend life, paving the way for a pill to increase lifespan, a daily newspaper reported.

The new findings build on decades of studies linking extreme diets in animals with extra months and years of life.

For example, cutting a mouse's calories by 30 percent can lead to it living 50 percent longer than usual.

Scientists are trying to work out what it is about near starvation that extends life, in the hope of creating a pill that mimics the process without drastic changes to diet.

The latest study looked at how cutting calories affects core body temperature -- an internal measure that is on average 37 degrees Celsius and usually higher than skin temperature.

Scientists gave thermometer 'pills', which record core body temperature when swallowed, to 24 people in their mid-50s who had cut their calorie intake by at least 25 percent for up to 15 years.

They also gave them to people of the same age who ate normally and a group of long-distance runners.

Those on calorie restriction diets were found to have the lowest core temperatures.

"The people doing calorie restriction had a lower average core body temperature by about 0.2c, which sounds like a modest reduction but is statistically significant and similar to the reduction we have observed in long-lived, calorie-restricted mice," said lead researcher Luigi Fontana.

"What is interesting about it is that the endurance athletes, who are the same age and are equally lean, don't have similar reductions in body temperature," he said.

"We know that people on calorie restriction diets feel colder than normal people because there is a lower metabolism and lower body temperature," he added.

Fontana said it is not clear whether severe calorie reduction, or something else, is lowering core temperatures.

But he believes a reduced temperature holds one of the keys to living to a ripe old age.